In the world of Lean/Six Sigma and process improvement, the term "critical to quality" is routinely used to help describe and then identify those points or tasks in a process where an interaction (mechanical or human) occurs, and where a "quality" measurement can be captured. For example, when a value-added document, product, service, etc. is actually given to the customer, this may easily be considered a "critical to quality" moment or transaction. As well, so might the moment when bad news is delivered, or the moment when customers are informed they cannot be served, or the moment they are informed their problem has been resolved.
Capturing these identified CTQs is a powerful way to understand how well you are serving the actual needs - and the critical to quality values of the customer.